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Dig Deeper: The Importance of Soil Sampling for Construction for Stronger Foundations

Written By
John Souffront
Last Updated - June 15th, 2023 7:19 AM

Are you planning to build a new structure or develop a piece of land? If so, you need to make sure that the foundation of your construction project is solid and stable.

As the saying goes, “ A building is only as strong as the foundation it sits upon’, which is why soil sampling for construction is crucial for any project.

By testing the soil before construction begins, engineers can assess the quality of the soil and determine the appropriate foundation design for the specific site. 

In this blog, we will explore the importance of soil sampling for construction and how it can help save time and money in the long run. 

Whether you’re a builder or a homeowner, understanding soil sampling for construction can ensure that your project starts on solid ground.

Man collecting soil

What is Soil Testing

Soil testing is a process that involves analyzing soil to determine its physical and chemical properties. 

It’s like giving the soil a check-up to see if it’s healthy and ready for its next big thing.

By collecting samples of soil and testing them with comprehensive laboratory analysis methods, soil sampling for construction reveals crucial information about the soil’s composition, nutrient content, pH level, and more. 

This information is vital for verifying the suitability of soil for various applications, such as construction, agriculture, and environmental remediation. 

So whether you’re building a new home or planting a garden, soil testing can help you ensure the success of your project by providing the necessary insight into the quality of the soil.

Why is the Soil Test for New Construction so Important?

Before beginning any construction project, it’s essential to conduct soil testing. But why?

Well, as mentioned before, the success of any construction project depends on the strength and stability of its foundation, which is directly affected by the quality of the soil. 

Soil testing helps engineers understand the physical and chemical properties of the soil on a construction site, such as its bearing capacity, compaction, and drainage. 

This information is crucial in determining the appropriate foundation design. It helps engineers to make sure that the building can withstand the weight of the structure and any external forces, making them earthquake-proof or flood-resistant

In short, as we have mentioned before, soil testing is like a health check-up for the soil. It helps us to identify any potential problems before construction begins. 

By taking this vital step, you can save time and money in the long run by avoiding costly foundation repairs and ensuring a safe and stable structure.

When Is It Done, And Who Does It?

Soil testing is a crucial step in construction and should ideally be done before starting any major construction work. Soil conditions can greatly impact the safety, stability, and durability of any structure.

So, if you’re planning a construction project, get the soil test done now itself. This will help you identify any potential issues with the soil that could affect the safety or longevity of your structure and allow you to take corrective measures before construction begins.

Depending on the scope and type of the construction project, a soil test might be necessary. In such cases, it’s always best to follow the regulatory requirements and get the necessary testing done as per their guidelines.

Now, who does it?

Soil testing for building a house is usually done by geotechnical engineers or soil testing laboratories. These professionals have the expertise and equipment to perform a variety of tests on soil samples to determine their properties and characteristics. 

They can also provide recommendations on the best foundation design and construction methods based on the results of the soil tests. It’s important to choose a reputable and experienced soil testing service to ensure accurate results and reliable recommendations.

Types of Soil Testing Before Construction

We are now pretty familiar with the concept of soil testing before construction and why land testing for buildings is important. So, let us explore various types of soil testing for construction.

Moisture Test

Did you know that moisture in the soil can impact its weight-bearing capacity and even state the likelihood of a termite infestation? 

Moisture refers to the amount of water present in soil and can be determined by calculating the soil’s water content. This crucial information is obtained by measuring the weight of a soil sample when moist and after it has been dried. 

As a rule of thumb, lower moisture levels tend to state stronger soil. Various methods can be used to test for moisture content to help determine the percentage of water in the soil. 

Soil moisture content is important for engineers and builders to design strong and durable foundations and structures. It also helps them to prevent termite damage.

Here are a few methods that are typically used for moisture testing:

Oven-Drying Method

When it comes to testing moisture content in the soil, the oven-drying method stands out as the most common and reliable. 

The oven-drying method involves taking a moist soil sample and heating it in an oven at approximately 110 degrees Celsius. 

After 24 hours, the dried sample is removed from the oven and weighed, allowing it to be compared to the weight of the original moist sample.

Girl putting soil in oven

The following formula is used to determine the water content of a soil sample:

w= (M2-M3)/(M3-M1) * 100


M1= Empty container’s mass with the lid

M2= Container’s mass with wet soil and lid 

M3= Container’s mass with dry soil and lid

The amount of soil sample required for this test varies depending on the particle size and gradation of the soil. 

By conducting a sieve analysis, engineers can determine the appropriate quantity of soil needed for the test. 

This information is vital for ensuring accurate results and can help builders and engineers design stronger foundations that can withstand external forces and avoid potential termite damage.

Radiation Method

Radiation isn’t just something from sci-fi movies; it’s also a real-life method for testing soil moisture content. Believe it or not, scientists can use radioactive isotopes to get the job done! 

This method works on a simple principle: the amount of energy lost by the neutrons is directly proportional to the quantity of moisture in the soil. 

By placing a device containing radioactive material, like cobalt 60, in a steel casing and lowering it into a borehole, scientists can accurately measure soil moisture content without even disturbing the soil.

Here’s how it works: 

The radio-active material emits neutrons, which scatter as they encounter the hydrogen atoms in the soil’s water. This scattering causes the neutrons to lose energy, and the amount of energy lost is directly proportional to the amount of water present in the soil. A detector placed in another steel casing is calibrated to give an accurate reading of the soil’s moisture content.

While this method is incredibly useful for in-situ testing, it’s important to use caution when working with radioactive materials. Proper shielding precautions must be taken to avoid any potential radiation problems. 

Despite the potential risks, the radiation method remains a valuable tool for engineers and scientists working to better understand the properties of soil and create stronger buildings and infrastructure.

Calcium Carbide Method

Calcium carbide method, also known as the speedy moisture tester, is a quick and easy way to determine the moisture content of soil using calcium carbide gas pressure.

This method works by measuring the pressure generated by the reaction between calcium carbide and water in a sealed container filled with soil. 

The pressure is directly related to the soil’s moisture content and is read on a gauge. It’s important to note that the reading obtained is on a wet moisture basis (m) and needs to be converted into water content on a dry mass basis using a simple calculation.

Formula to convert wet moisture basis (m) into dry mass basis:

w = [m/(100-m)] * 100

With the Speedy moisture tester and a little bit of math, you can quickly and accurately determine the moisture content of soil for your construction or engineering project.

Alcohol Method

The alcohol method is a speedy way to measure the moisture content of the soil. It works on the same principle as the oven-drying method, but instead of heat, we use methylated spirit to dry out the wet soil.

While it may not be as precise as other methods, the alcohol method is a great choice for quick and easy field tests. 

Just be aware that if your soil is chock-full of clay, gypsum, calcareous matter, or organic matter, this method may not be the best fit.

To calculate the percentage of water content in your soil, use this formula:

W = [(W2 – W3) / (W3 – W1)] * 100


W = the water content percentage

W1 = the mass of the dish in grams

W2 = the mass of the dish with wet soil in grams

W3 = the mass of the dish with dry soil in grams

Sand Bath Method

When you’re out in the field and need to determine the moisture content of the soil, the Sand Bath Method is here to save the day. No electric oven is required – just a tray of sand about 3 cm high and a container filled with wet soil.

Simply place the container on the sand bath and heat it up while stirring, with a few white papers on top of the soil. As the soil dries out, the papers will turn from white to brown, indicating that the soil is dry and ready for testing.

With the dry soil in hand, you can use the same equation as the oven-drying method to calculate the water content percentage, which is:

w= (M2-M3)/(M3-M1) * 100


M1= Empty container’s mass with the lid

M2= Container’s mass with wet soil and lid 

M3= Container’s mass with dry soil and lid

Torsion Balance Method

The torsion balance method is a handy technique which perfect for soils that re-absorb moisture quickly after drying, providing highly accurate and rapid results in no time. 

By weighing and drying your soil sample at the same time, the Torsion Balance method eliminates the need for multiple steps and time-consuming calculations. 

Plus, with its calibrated balance, you can get a direct measurement of your soil’s water content with ease. Don’t settle for slow and inefficient methods – try the Torsion Balance method for quick and precise results.

After performing the Torsion Balance method, you’ll obtain the water content of your soil sample based on its wet weight, which is represented by w’. Using this value, you can then calculate the weight of water by using the formula:

w = w’ / (1 – w’)

With the torsion balance method, you can get the moisture content of the soil in just 15 to 30 minutes. Keep in mind that the test result can vary based on the soil type and the amount of moisture in it. 

Pycnometer Method

The pycnometer method is fast and efficient, but it works best for coarse-grained soils whose specific gravity is accurately known.

So, what exactly is a pycnometer? 

It’s a nifty little device that looks like a density bottle with a capacity of 900 mL. The bottle has a brass conical cap that serves as a cover, and a rubber washer is placed inside the cap to prevent water leakage.

To calculate the water content of the soil sample, scientists use the following formula:

w = (M2 – M1)/(M3 – M1) – (M4 – M1) x G


M1 = the mass of the empty pycnometer.

M2 = the mass of the pycnometer with wet soil.

M3 = the mass of the pycnometer and soil filled with water.

M4 = the mass of the pycnometer filled with water only.

G = the specific gravity of soil.

Atterberg Limits Test 

The Atterberg limits are a set of measurements that are used to determine the critical water contents of fine-grained soil. These limits include the shrinkage limit, plastic limit, and liquid limit.

The water content of the soil plays a crucial role in determining its behavior and can place it in one of four states: solid, semi-solid, plastic, or liquid.

When the soil is in a solid state, it is dry and compact and doesn’t easily deform. In a semi-solid state, the soil has a slightly higher water content and can be molded but still retains its shape.

As the water content increases, the soil can reach a plastic state, where it can be easily molded and shaped, much like modeling clay. At the liquid limit, the soil behaves like a liquid, with little to no shear strength.

Understanding the Atterberg limits of a soil sample can provide valuable insights into how it will behave under different conditions. 

For example, construction professionals and engineers can use this information to determine the suitability of a particular soil for building foundations or structures.

Liquid Limit Test

The liquid limit is an important property of soil that tells us at what point it starts behaving like a liquid while still retaining a small amount of shear strength. 

To determine the liquid limit of a soil sample, a device called Casagrande’s liquid limit device is used.

In this device, a groove is made in the soil sample, and a standardized tool is used to strike it, causing it to close. 

The number of blows required for the groove to close in just 25 strikes is recorded, and this number is known as the “N-value.”

Since getting exactly 25 blows in a single test can be challenging, 3 to 4 tests are typically conducted, and the N-value is determined for each test. 

A semi-log plot is then drawn between the log of N-values and the corresponding water content.

The liquid limit of the soil sample is the water content at which N equals 25, as obtained from the plot. 

The formula commonly used for the liquid limit test is:

LL = k * WN

If the liquid limit of the soil is too high, it may be unsuitable for building a stable foundation or structure.

Plastic Limit Test

When we talk about the plastic limit of soil, we’re referring to the point at which it starts behaving like a plastic material. 

This is determined by measuring the moisture content of the soil at which it crumbles when it’s rolled into threads that are 3.22 mm in diameter.

There are established test methods for determining the plastic limit of soil, outlined in the ASTM D4148 standard. 

These methods ensure consistency and accuracy in measuring the plastic limit of different soils.

Formulas used to determine the plastic limit of soil are

  • Flow index, If = (W1-W2)/ log10(N2/N1)
    W1 = Moisture content in percentage corresponding to N1 drops and
    W2 = Moisture content in percentage corresponding to N2 drops
  • Plasticity Index, Ip = WL – WP
  • Toughness Index = Ip/If

Shrinkage Limit Test

The shrinkage limit of soil refers to the amount of water that’s needed to fill all the tiny spaces between soil particles, leaving no more room for water to seep in. 

It’s like when a sponge is completely saturated with water and can’t absorb anymore.

When the water content of the soil is reduced below the shrinkage limit, the volume of the soil won’t decrease any further. 

This limit can be determined by using a formula that takes into account the relationship between the water content and the volume of soil.

Ws = [(M2 – M1)n – (V1 – V2) Pw / M2] * 100


M1 = initial mass

V1= initial volume

M2= dry mass

V2= volume after drying

Pw = density of water

Dry Density Test

Dry density is a fundamental property of soil that measures the weight of soil particles in a given volume of sample. It’s an essential parameter for engineers to determine the load-bearing capacity of soil and design foundations accordingly.

The dry density of soil is influenced by two factors – Void Ratio and Specific Gravity. Void Ratio is the ratio of the volume of voids to the volume of solids, while Specific Gravity is the ratio of the density of soil particles to the density of water.

The dry density test provides valuable information to classify the soil as dense, medium, or loose. It’s a crucial step in evaluating soil suitability for construction projects.

There are different methods to calculate the dry density of soil, such as The Core Cutter Method, Sand Replacement Method, and Water Displacement Method. 

Each method has its unique advantages and limitations, and the choice of method depends on the specific requirements of the project.

Core Cutter Method

The core cutting method is a simple yet effective way to determine the dry density of soil. 

Here’s how it works: 

A cylindrical core cutter with specific dimensions is used to extract a soil sample. The weight of the soil sample is then measured and recorded for further analysis.

To determine the dry density, the water content of the soil sample is first calculated. Once that’s done, the dry density can be easily determined. 

This method is commonly used by engineers to figure out the maximum dry density and optimum water content of compacted soil.

Sand Replacement Method

In this method, engineers first dig a hole in the ground to obtain a sample of the soil they want to test. The engineers then carefully fill the hole with uniform sand of known dry density. This helps them determine the volume of the hole since they know the mass and dry density of the sand they used to fill it.

Next, the engineers weigh the excavated soil sample and record its weight. From there, they can calculate the dry density of the soil using a formula that takes into account the volume of the hole, the weight of the excavated soil, and the weight of the sand used to fill the hole.

This method is particularly useful for large-scale projects, as it can provide a quick and accurate assessment of the dry density of soil without having to transport samples to a laboratory for testing.

Water Displacement Method

The water displacement test method is a handy technique for measuring the dry density of cohesive soil. This method requires a specimen of a particular shape, and it’s commonly used to evaluate the in-place dry density of soil.

To perform this test, the soil sample is first trimmed to achieve a uniform shape. Then, it’s coated with a water-resistant material, usually wax. This coating ensures that the sample is impervious to water.

Next, the volume of the soil sample is determined by measuring the volume of water displaced by the specimen. This volume, along with the weight of the sample, is used to calculate the dry density of the soil.

The formula used to calculate dry density with the water displacement method is

Dry Density=(M/V)/1+w


M = Mass of Wax

V = Volume of Wax

w = Water Content

Specific Gravity Test

The specific gravity test tells us the void ratio and degree of saturation of the soil. Basically, it gives us an idea of how much air and water are present in the soil.

Now, when it comes to using soil for construction, there are some specific things to look for. 

One important factor is the specific gravity value of the soil, which should ideally be between 2.65 to 2.85. 

If the value is lower than 2, it could mean that there’s a lot of organic matter and porous stuff mixed in with the soil. 

On the other hand, a value above 3 might indicate the presence of heavy materials in the soil.

So, what you want for construction is soil that has low amounts of organic matter, porous materials, and heavy substances. 

That way, you can make sure that the soil is strong and stable enough to support buildings and other structures.

Compaction Test (Proctor’s Compaction Test)

The compaction test, also called the proctor’s compaction test, is used by engineers to land testing for buildings and study how soil compacts when air voids are removed by pressing it together.

The test results reveal two important values: the maximum dry density and the optimum water content of the compacted soil. 

These values are crucial in determining how to compact the soil efficiently and effectively for construction purposes.

Process of Soil Testing for Construction

Basically, the engineers arrive at the site with their tools and team and start digging holes in the soil to collect samples. 

These holes may not always be deep and can be easily dug with hand tools, but sometimes, depending on the soil type, they may need to dig a hole as deep as 7-10 feet.

Once the samples are collected, they are taken to the geotechnical labs, where they are tested for various factors like composition, reactivity, salinity, moisture, and much more.

Based on the test findings, the soil engineer(s) will then make recommendations that could range from the required depth for the foundation to changes in the building’s entire design.

It’s important to remember that the strength and stability of a building can be drastically affected by the properties of the soil. 

So, it’s crucial to follow the soil test report’s directions and recommendations religiously while making the construction plan to ensure the safety and longevity of the building.

Tackling the Tough Results of a Soil Test with Smart Solutions!

Your soil test report might reveal the presence of clayey soil or sand, and in such cases, it might not be wise to choose a simple rubble foundation for your house. 

But what can you do? Let’s take a look at some possible outcomes and solutions based on your soil test results.


If your soil test report indicates the presence of clay in the soil, you might encounter some issues. The bearing capacity of saturated clay is typically low, resulting in weak foundations. 

However, you can address this issue to a certain extent by using compaction techniques to remove air from the soil pores. For this type of soil, it’s more appropriate to use deep foundations.

Another issue you might face with clay soil is its low shear strength, which means it can’t sustain much stress when wet. 

This results in a high possibility of soil consolidation in soft clays. To address this problem, you can try lowering the water table, pre-loading the soil, or driving piles to rock.

Additionally, swelling can occur in clay, which can alter the formation of the soil and cause foundation expansion or swelling. 

To prevent this from happening, you can maintain a constant water table, treat or stabilize the soil, or include swell pressure in the design. 

Another option is to mechanically change the nature of the soil, but that might be an expensive solution.

While clay can pose a challenging problem for your project, its nothing that can’t be taken care of with the right strategy.


Have you ever noticed that sometimes foundations of buildings tend to settle excessively in wet and loose soils? This can lead to differential settlement, a serious issue. 

But don’t worry; there are ways to resolve this problem. 

One way is to compact loose sands. It will help to some extent. Another method is to lower the water table, which results in sand densification.

However, sandy soils come with their own challenges. For example, the confining pressure of sand is usually low. This affects the bearing capacity of the foundation. 

To counter this, deep foundations are the way to go. The compaction of sand can also improve the bearing capacity as it increases cohesion and friction.

Overall, while sand in the soil presents some challenges, there are effective solutions available to address them. 

With the help of appropriate techniques and strategies, you can ensure that your foundation remains strong and stable, even in the presence of clay or sand. 

So don’t let a challenging soil test result discourage you – with the right approach, you can build a solid foundation for your project.

Final Thoughts

Soil testing is an essential step that cannot be overlooked when it comes to construction. Some contractors may skip a soil test for house construction to save money or because they don’t realize how important it is. This can be a problem.

This can be a dangerous mistake, as building on unstable soil can have disastrous consequences.

In fact, soil testing is so important that many governments around the world have made it a legal requirement before construction can begin. 

This is because soil conditions can vary greatly even within a small area, and it’s essential to know what you’re building on to ensure the safety of the project and the people who will be using it.

Ignoring soil testing can be dangerous, and frankly, it’s not worth the risk. That’s why it’s important to work with a reliable and trustworthy construction company like Souffront .

We understand the importance of soil testing and can guide you through the process to make sure your project is safe and secure. 

So, invest your time and money wisely, and let us take care of all your construction worries. Contact Souffront today for the right information and expert guidance.

John Souffront

John Souffront is a seasoned leader in the construction and engineering industry, with over a decade of experience at the helm of Souffront Construction & Engineering. Known for his unwavering commitment to excellence and innovation, John has propelled his firm to the forefront of the field, delivering cutting-edge solutions for complex projects around the country.

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